Ventilating apparatus for a paper machine



March 25, 1969 BLOMGREN ETAL 3,434,224

VENTILATING APPARATUS FOR A PAPER MACHINE Sheet Filed June 5, 1967 q. R O T N E V m 2 2 m Hull- I F I 7 m I BLOMGREN ATTYS-,

March 25, 1969 1.. BLOMGREN ETAL 3,434,224

VENTILATING' APPARATUS FOR A PAPER MACHINE Sheet 3 of 2 Filed June 5, 1967 INVENTORSI LARS BLOMGREN AKE JOHANSSON W 799W l t h 1| United States Patent 0 Int. c1. F26!) 13/08 US. Cl. 34-114 1 Claim ABSTRACT OF THE DISCLOSURE A ventilating apparatus for the dryer section of a paper machine, said apparatus including rotatable air ducts on each side of the dryer section, which air ducts are provided with openings to discharge adjustable jets of ventilation air in order to control cross-flow tendencies inside a casing for the dryer section and thereby to prevent uneven drying profile of the paper web being dried.

The present invention relates to the apparatus for the ventilation of a paper machine, comprising a casing for the dryer section of the paper machine, which casing includes roof, side walls and end walls, means for the supply of ventilation air to the casing and means for the removal of ventilation air from the casing.

It is known in the drying of paper by cylinder drying machines to provide the dryer section of the paper machine with a casing and to supply to as well as to remove from the casing controlled amounts of ventillation air. The casing offers the advantage that the temperature and moisture in the machine-room surrounding the paper machine can be maintained lower than without a casing, which renders the working conditions for the staff more comfortable, and that the air temperature and hir humidity in the dryer section of the paper machine can be maintained higher than without a casing, which results in an improved heat economy.

It is also generally known that it is difficult to dry the paper web uniformly across its width in spite of the casing of the dryer section of the paper machine. As a rule, the drying result is worse in the middle of the web than at its edges but a very usual phenomenon is also an uneven drying profile, at which the drying of one edge is worse than that of the other edge. In most cases an uneven drying profile is due to the fact that air flows across the paper web between the drying cylinders, whereby the paper web edge, at which the air flows in, is dried more than the edge, at which the air leaves the web.

In the common types of casing the ventilation air is supplied through the basement-floor below the dryer section or immediately below the usual lower drying felts, and removed through a gap or openings along the longitudinal central line of the roof. This is a natural method in view of the decreasing density of the air on its passage through the dryer section, which partly is due to its mixing with evaporated water vapour and partly to its heating by contact with the heated drying cylinders. In this way, the possibilities of self-draught are utilized.

A cylinder dryer section, however, is never symmetric with respect to the central portion of the paper web, because on one side thereof there are arranged the transmissions for the operation of the drying cylinders and the steam fittings for the heating of the cylinders. Said fittings comprise a great number of hot pipes, which produce thermal forces tending to press up great amounts of air on this side. Under these conditions an air flow across the machine easily can develop. The vertical flow areas on both sides of the machine can have difierent size,

3,434,224 Patented Mar. 25, 1969 which also contributes to the development of cross flow.

It is an object of the present invention to provide a ventilating apparatus for the dryer section of a paper machine, by which apparatus the cross-flow tendencies and thereby the uneven drying profile can be controlled.

A more specific object of the invention is to provide means for the supply of ventilation air comprising members located on each side of the dryer section between same and the side walls and distributed along the length of the dryer section, which members can eject directed jets of ventilation air, which by their impulse flow counteract undesirable air flows.

Other characterizing features of the invention become evident from the description of the accompanying drawing figures, by way of example. In the drawings:

FIG. 1 is a cross section through the dryer section in a paper machine provided with a ventilation apparatus according to the invention;

FIG. 2 is a side view of the air-supplying members as seen from the line 2-2 of FIG. 1; and

FIG. 3 is a side elevation view of the dryer section as seen from the left of FIG. 1 with a side wall removed and with parts shown in section.

The drying section comprises a machine stand 1 and a number of drying cylinders 2, about which the paper web is directed in a zigzag path. The machine stand is supported on so-called supporting strands 3 of concrete. Above the machine stand 1 a light-weight frame 4 is mounted carrying the upper portion of the casing. The right-hand portion of the machine stand 1 includes the transmission for the operation of the drying cylinders. To the right of the transmission the steam and condenser tubes 5 for the heating of the drying cylinders are located. The casing comprises a roof 6, a side wall 7 on the machine operators side, a side wall 8 on the driving side of the machine and two end walls (not shown). For making the dryer section accessible for operation, a number of liftable doors 9 and a number of slidable doors 10 are provided in the side wall 7 on the operators side, and a number of slidable doors 11 are provided in the side wall 8 on the driving side.

It is not possible for a reasonable price to make the doors in the casing fully tight. Certain areas of leakage must therefore be accepted. Furthermore, the casing must be provided with holes for a great number of pipes and cables. The leakage areas therefore can have a relatively great size. In order to avoid the outflow of hot moist air from the casing through the leakage areas into the machine room one tries to maintain some vacuum within the casing, and it is calculated that 30% of the air amount exhausted from the casing is supplied as leakage through unavoidable openings.

For removing by ventilation the water vapour, which evaporates from the drying paper web, the casing is supplied with heated ventilation air through a passage 12, which extends along the central line of the machine in the basement floor below the dryer section. The upper wall of the passage, along the length of the dryer section, is provided with a number of slots 13 for distributing the ventilation air supplied through the passage. The overpressure in the passage is small, but the area of the outflow slots is large so that relatively great amounts of air are supplied at a low speed. For the removal of ventilation air the roof is provided in its centre with a gap 14 to an overlying collecting passage 15, which is connected to exihaust fans 16.

According to the invention the means for the supply of drying air also comprise circular impulse air ducts 17, 18 located along the side walls 7, 8 between same and the machine stand 1. The ducts 17, 18 are divided into sections, which are rotatable in relation to each other for rendering possible the directing of a slot 19, 20 provided in every section. The impulse air ducts are connected by ducts 2 1, 22 to the pressure side of fans 23, by which hot air is sucked from a heat recovering unit 24.

During operation, in the impulse air ducts 17, 18 an overpressure of the magnitude 20 mm. H O is to be maintained, which imparts to the air leaving the ducts in the form of directed jets a speed of about 20 m./sec. The impulse, or more correctly the impulse flow of the air jets, by friction against the surrounding air, is transferred to the same, which thereby is caused to participate in said ejection. In this Way, it is possible to influence the air flows within the casing.

The flow condition desired to be obtained is characterized by the freedom from horizontal cross flows through the dryer section past the paper web. Cross flows can be caused a.o. by the thermally caused air flow about the steam fittings 5 or by disturbances from leakage flows. In the event of a cross flow from the right to the left in the figure, for example due to thermal upward flows about the steam pipes, the flow can be counteracted and neutralized by placing the outflow openings 19, 20 of the impulse air ducts 17, 18 in the positions shown in the figure. The air jets from the right-hand duct 18 thereby bring about an air motion, which neutralizes the tendency for overpressure on the right-hand side of the dryer section, which gave rise to the cross flow. In a corresponding way the jets from the left-hand duct 17 neutralize the tendency for sub-pressure found to the left of the dryer section. In the case of varying tendencies along the length of the dryer section and seotionalizing of the ducts 17, 18 provide the possibility of individual adjustment.

If it is desired to make the adjustments in a still more improved way, the area of the openings 19, 20 in the impulse air drums can be made adjustable.

We claim:

1. A ventilating apparatus for the dryer section of a paper machine, said apparatus comprising a casing for said dryer section, including roof, side walls and end walls; means for supplying ventilation air to the casing; and means for exhausting ventilation air from the casing, said air-supplying means including fan means and horizontally extending air ducts loacted on each side of the dryer section between same and the side walls and having a plurality of duct sections along the length of the dryer section, said air duct sections being connected to the pressure side of said fan means, and being provided with openings to discharge jets of ventilation air, said duct sections being rotatable in relation to each other to adjust said jets.

References Cited UNITED STATES PATENTS 1,515,431 11/1924 Cobb 3484 2,000,546 5/1935 Woodsorne 34-414 XR 2,977,686 4/1961 Stout 34-114 CARLTON R. CROYLE, Primary Examiner.

ALLAN D. HERRMANN, Assistant Examiner.

US. Cl. X.R. 34-84 

